Electrophotographic material and method



United States Patent 41 Claims. ci.' 96-1) This invention relates to photographic reproduction and more particularly to electro-photographic processes, namely processes in which an electrostatic latent image is produced by utilising the property of photoconduction (i.e., a variable conductivity dependent on the intensity of illumination). The electrostatic latent image may be produced in a conventional exposure operation, for example by means of a lens-projected image or by contactprinting techniques, whereby a non-visible electrostatic charge pattern (the so-called electrostatic latent image) is created on a surface, in which pattern the charge density at any point is related to the intensity of illumination obtaining at the point during the exposure. The latent image may be developedi.e., rendered visibleby means of an electroscopic powder, such as a coloured synthetic resin powder, and the resulting visible image may be fixed by rendering the powder permanently adherent to a support on which the image is desired, for example in suitable cases by heating to soften or melt the powder particles and/ or the surface of the image support, or by application of an electric field, or with volatile solvents.

In electro-photographic processes the electrostatic latent image is commonly formed on the surface of a photoconductive insulating layer carried on a support. For example, material comprising such support and photo-conductive layer may be sensitized by applying a uniform surface charge to the free surface of the photoconductive layer, for example, by means of a corona discharge, which charge is retained owing to the substantial insulating character, i.e., the low conductivity, of the layer in the dark. On exposure as described above, the photoconductive property of the layer causes the conductivity to increase in the illuminated areas to an extent which is proportional to the intensity of illumination. This results in a leakage of the surface charge in the illuminated areas while the charge in the unilluminated areas remains. This is what constitutes the aforementioned charge pattern or elastrostatic latent image.

Electro-photographic processes have become of increasing importance in recent years, especially in connection with ofiice duplicating processes where, otiering as they do a wholly dry copying process, they are usually preferable to other types of photo-copying. Consequently, there has been much interest aroused and much eiiort has been made to obtain suitable materials for making the support and photoconductive insulating layers used in such processes.

Various proposals in regard to such materials have been made in an effort to fulfill modern requirements with regard to range of use, reliability, simplicity in handling, potential light sensitivity and storage qualities. Among those photoconductive substances used hitherto, selenium has been the most notable, although many other materials have also been used. However, all these prior materials had various disadvantages which have now been overcome by the present invention.

Generally described, the present invention provides a material for use in electrophotographic processes, which is capable of being rendered light sensitive by applying an electrostatic charge thereto. It comprises a support carrying a photoconductive insulating layer, which layer comprises at least one photoconductive substance consisting of a 2,5-bis (para-aminophenyl)1,3,4-oxadiazole compound. In preferred embodiments of the invention, the said photoconductive substance or at least one of the said photoconductive substances is of the general formula:

( s NN R Rr 7 o R4 (3) R5 NN alkyl.

11 o alkyl in which R represents hydrogen or an alkyl, acyl, or cycloalkyl radical,

R represents hydrogen, R represents an alkyl or acyl radical, R represents an alkyl radical,

and

R represents hydrogen or 'alkyl.

Compounds of these general formulae include, for example,

2,5 -bis- [4-aminophenyl- 1 ]-l ,3 ,4-oxadiazole, the

2,5-bis- [4'-monoalkylamino-phenyl-( 1 ]-1 ,3,4-

oxadiazoles,

the 2,5 -bis- [4-dia1kylamino-phenyl-( l) ]-l ,3,4-

oxadiazoles,

the 2,5 -bis- [4-monoacylamino-phenyl- 1') -1,3,4-

oxadiazoles,

to mention only a few of the most important.

The 2,5-bis-(p-amino-phenyl)-1,3,4-oxadiazole compounds can generally be prepared by methods known per so from 2 mols of the appropriate para-aminobenzene carboxylic acid and 1 mol of a hydrazine salt in the presence of dehydrating agents, such as oleum or polyph0s' phoric acid.

The 2,5 bis-(para-amino-phenyl)-l,3,4 oxadiazole compounds have very good photoconductivity and are particularly suitable for the preparation of homogeneous layers having a long shelf-life. The compounds are colourless and fiuoresce in daylight or in ultraviolet light.

Compounds which are particularly adaptable to the present invention have the following formulae:

FORMULA 1 H; O N-N C H FORMULA 5 methylene chloride or ethylene-glycol-monomethyl-ether. H2 N H H2 H2 Mixtures of two or more photoconductive substances may be used, also in such solution. Mixtures of solvents may L I/ 7 also be used. It is also possible to employ the photocon- 7 Q 5 ductive substances in association with other organic pho? .C-C toconductive substances; E It has further been found advantageous in preparing the FORMULA 6 H H synthetic polymer or other organic colloid, forexample: H2 H2 I V V H (a) natural and synthetic resins, e.g. balsam resms, Q phenol resins and other resins modified with colophony, i (5-H 0H coumarone resins and indene. resins and the substances covered by the collective term synthetic lacquer resins,

7 H2 Hg which includes processed natural substances such as cellu- FORMULA 7 lose ether,'see the Kunsts'tofitaschenbuch (Plastic Pocket H703 @3117 'Book) published by Saechtling-Zebrowski (11th edition, II II 1955, page 212 onwards); O V (b) polymers (including co-polymers) such as the poly- H;C3 0 3 vinyl chlorides, polyvinyl acetate, polyvinyl acetals, poly- FORMULA 8 vinyl alcohols, polyvinyl ethers, polyacrylic and polymeth- H N N H acrylic esters, and polystyrene and isobutylene polymers; l (c) polycondensates, e .g., polyesters, such as phthalate 7/ resins, alkyd resins, maleic acid resins, colophony esters of H3000 V O C 00113 mixed higher alcohols, phenol-formaldehyde resins, partic- FORMULA 9 'ularly colophony-modified phenol-formaldehyde conden- 1 H sates, urea-formaldehyde resins, melamine-formaldehyde H H condensates, aldehyde resins, ketone resins of whichpar- N C ticular mention is to be made of AW 2 resins of the firm f HSCOG/ O 7 000B, Badische Anilinund Sodafabrik, xylene-formaldehyde FORMULA 1O resins and polyamides; and v C1 01 (d) polyadducts, such as polyurethanes. H N B When the photoconductive substances are employed in l association with organic colloids, the proportion of resin O H to photoconductive substance can be varied very greatly. 0 3 7 The use of mixtures of approximately equal parts by FORMULA 11 Weight of resin or other colloid andphotoconductive subr l 7 stance has been found generally advantageous. When V 00-}: such mixtures of approximately equal parts by weight of \C2H5 resin and photocond uctive substance are used, in most FORMULA 12 cases said solutions give homogeneous transparent colour- V less layers on drying that can be considered. as solid H5C2\ H 02m solutions. i

Nd\ C A The support may be of any material suitable for use in H703 0 electrophotographic processes, for example, aluminum or FORMULA 13 other metal plates or foils; glass plates; paper sheets or H592 N N 7, C235 Webs, or plastic foil, especially foils made of electrically OJl conductive resins. If paper is to be used as support for the PhOtOCODdUCtlVC layer, it is preferable that it shall have H CQC p 000113 been pretreated against penetration by the coating solu- FORMULA 14 tiori, for example with methylcellulose in aqueous solu- N N tion;.polyvinyl alcohol in aqueous solution; a solutionin LO M acetonegand methyl-ethyl-ketone of a mixed polymer of I V acrylic acid methyl ester and acrylomtrile; or with solutrons of polyamides in aqueous alcohols. Aqueous dis- FORMULA 15 persions of other substances suitable for the pretreatment V of the paper surface may also be used. 7 V (CH3)2NC C O-C NHC3H1 Solutions of the photoconductive substances in organic solvents as described above, with or Without the added 1 organic colloids aforementioned, can be applied .to the FORMULA supports in known manner (for example, by spraying, direct application, or whirl coating), and thev supports ,c,NH C o CC NHCHH7 thus coated, dried, so that an even photoconductive layeris formed thereon.

' While the layers are, in themselves, non-light-sensitive, F M A '17 by applying a positive or negative electrostatic charge F thereto, by means for example, of a corona discharge, the c N(CH3)2 layers are rendered light-sensitive and can be used with 7 long-wave UV. light of 3600 to 4000 A.U. in producing area i4? The photoconductive substances which are used accordphotoconductive insulating layers'to use the photoconduc tive substance or substances in association with a resin,

electrostatic latent images as described above. Very good images may be obtained by a short exposure under a master to a high-pressure mercury vapour lamp.

3 ing to the invention for the preparation of the photoconductive insulating layers are preferably so used in solution I in organic solvents such as for example benzene, acetone,

Although the layers when charged are but'slightly sen sitive to light in the visible spectrum, it has further. been.

Reference (Schultz Farbstotltabellen, 7th edn., vol. 1 (1931)) Dyestufi Group Dyestufi compound Triarylmethane dyes Xanthene dyes:

Rhodarnine B No. 864 (p. 365). Ehodamine 6G No 866 (p. 366) Rhodarnines Rhodamiue G extra No 865 (p. 366) Sulphorhodamine B True acid Eosin G.

EosinS No 883 (p 3 a ses as *ry osin" o 886 p Iflalems Phlorin No 890 (p 378) Rose Bengal No 889 (p Fluoresceim (p. 73). Thiazine dyes Methylene blue No. 1038 (p. 449).

Acridine yellow- N0. 901 (p 383). Aeridine dyes Aeridine oran e N0 908 (p 387) ligrypafiavilumun bo. ED. macyauo l 0. p. Qumolme dyes {Cryptocyanine No 927 (p 397). Quinone dyestufi's No 1141(1) 499) Anthraquinones N0 1145 (p 502) N0 1148 (p 504) Cyanine dyes Hill S S(])Hz H C-CH-CH=CHC CH2 l CH3 H3C $040113 The layer-carrying supports may be utilized for the production of images by electrophotographic means, for example, as follows: When the photoconductive layer has been charged, by means of, for example, a corona discharge with a charging apparatus maintained at 6000 volts, the thus sensitized layer is exposed to light under a master or by episcopic or diascopic projection and is then dusted over in known manner with a suitable developing agent such as a resin powder coloured with carbon black. We prefer a resin developer obtained by fusing parts by weight of polystyrene (K-Wert 30 parts by weight of a maleic acid resin modified with rosin and sold under the registered trade-mark Beckacite K 105, and 3 parts by Weight of carbon black, and subsequently finely grinding the fused mass. The image that now becomes visible can easily be wiped off, and therefore needs to be fixed; it can, for example, be heated briefly to approximately 120 C. by means of an infra-red radiator. The temperature need not be as high as this if the heat treatment is carried out in the presence of vapours of solvents such as trichloroethylene, carbon tetrachloride or ethyl alcohol. The powdered image can also be fixed by means of steam. From positive masters, positive images of good contrast are produced.

After being fixed these electrophotographic images can be converted into printing plates; the support, e.g., the paper or plastic foil, is wiped over with a solvent for the photoconductive layer, e.g., alcohol, or acetic acid, and then rinsed with water and rubbed in with greasy ink in known manner. In this Way positive printing plates are obtained which can be set up in an ofiset machine and used for printing. They give very long runs.

If transparent supports are used the electrophotographic images can also be used as masters for the production of further copies on any sort of light-sensitive sheets. In this respect the photoconductive compounds to be used as provided by the invention are superior to substances used hitherto, such as selenium or zinc oxide, inasmuch as the latter give cloudy layers because solid solutions cannot be produced with such materials and only suspensions are possible.

' Jhere translucent supports are used for photoconductive layers such as are provided by this invention, reflex images can also be produced. The possibility of a reflex copy is also an advantage over the known art.

Moreover the photoconductive layers prepared as provided in the invention have a further important advantage in that they can be charged positively as well as negatively. With positive charging the images are particularly good while there is negligible evolution of ozone, which is considerable with negative charging.

The invention and methods of practicing the same are further illustrated in the following specific examples, in which reference is made to the chemical formulae listed above:

xample 1 A solution containing 1 g. of 2,5-bis-[4-dimethylaminophenyl-( l')]-l,3,4-oxadiazole, corresponding to Formula 1, and l g. of indene resin (e.g., the product obtainable from Farbenfabriken Bayer AG, Leverkusen, under the trade named TC Earz) dissolved in 30 g. of benzene, is applied to a paper foil the surface of which has been pretreated to prevent the penetration of organic solvents. The treated paper is then dried.

On this treated paper, direct images are produced by the electrophotographic process whereby, by means of a corona discharge apparatus, the paper is given either a positive or a negative electric charge; it is then exposed under a positive master to a high-pressure mercury lamp and dusted with a resin powder coloured with carbon black. The finely powdered resin adheres to those parts of the layer that were not exposed to light during exposure and a positive image is developed: this is heated slightly and thereby stabilised (fixed). It shows good contrast since the background of the paper is brightened by the substances that have been applied thereto.

If instead of paper as above, a suitable transparent plastic foil or transparent paper is used as support for the photoelectric layer, the images produced are suitable as master-copies for duplication processes by means of any sort of light-sensitive sheets.

The compound corresponding to Formula 1 may be produced as follows: 36 g. of 4-dimethylamino-benzoic acid are introduced, with cooling, into a solution of 13 g. of hydrazine sulphate in 250 g. of oleum (24% S0 The reaction mixture is then heated with agitation to 79 C. for 23 hours; it is then poured onto ice and, with cooling, made slightly alkaline by means of sodium hydroxide solution; the precipitated condensation product is separated from the mother liquor. The oxadiazole compound formed (Formula 1) is washed and dried; it is in the form of a light powder, which in solution gives bluish fluorescence in ultra-violet light. The compound has a melting point of 225227 C.

Example 2 image in carbon black-resin powder, and recharging by means of a corona discharge is carried out, the carbon black-resin image is transferred to transparent paper or transparent plastic foil, the image obtained can be further copied, for example on diazo photoprinting paper.

Formula 1. The reaction mixture is heated with agitation for three hours to 6070 C.; it is then poured on to ics 'and, with cooling, made slightly alkaline with sodium hydroxide; the precipitated condensation product is separated from the mother liquor. It is purified by recrystal-. lization from 96% ethyl alcohol and melts at 152-153 C. Instead of oleum, polyphosphoric acid can be employed as condensation agent in the above-described process. In

such case 13 g. of hydrazine sulphate are introduced into 200 g. of polyphosphoric acid at room temperature and then 42 g. of 4-diethylamino benzoic acid are added and the mixture is heated for two hours to 80 C. When everything hasgone into solution the syruplike condense- "tion product is poured on to ice. The precipitate is sepa-' rated from the mother liquor, rinsed in water and recrystallized from 96% alcohol.

' Example 3 1.5 g. of the compound corresponding to Formula 1, 0.5 g. of the compound corresponding to Formula 2, and

1 g. of a synthetic resin produced .by condensation'of cyclohexanone with methylcyclohexan'one (c.g. the product. of Badische Anilin und Soda-Fabrik, Ludwigshafen,

known as Kunstharz AWZ) are dissolved in 50 g, of benzene and then applied to paper which has been prepared in accordance with U8. Patents Nos. 2,534,650, 2,681,617, or 2,559,610. The layer left on the paper after evaporation of the solvent adheres firmly to the surface. .With coated paper of this kind, images with good contrast on white ground are produced by the'electrophotographic process as described in Example 1.

Example 4 0.5 g. of 2,5-bis-[4-isoamylamino-phenyl-(1")]-l,3,4-

' oxadiazole corresponding to. Formula 3, 1.5 g of 2.5-bis- [4' n propylamino phenyl (1')] 1,3,4 oxadiazole corresponding to Formula 4, 1 g. ofcolophony-formalde- 'h yde resin (e.g.,' that marketed by Farbenfabriken Bayer AG, Leverkusen, under the registered trade-mark Corepal 140?) and 0.01 g. of methylene blue are dissolved I in 30 g. of benzene and the solution is applied to a paper foil of the kind employed in Example 1 and dried. The paper coated in this manner is electrically charged in known manner and can be discharged by exposure to a high-pressure mercury vapour or to an incandescent lamp,

whereby, if a master is interposed, an image of the master copy is produced. The addition of the methylene blue 1 as sensitizer enables theexposure time to be reduced to a fifth of that required in'the absence of the sensitizer.

The compound corresponding to Formula 3 may be obtained by the introduction with cooling of 43 g. of 4-isoamylamino-benzoic acid into a solution of 13 g. of hydrazine sulfate in 255) g. of oleum (24% S followed by further treatment of the reaction mixture in analogous manner to that given in Example 1 for the compound j with Formula 1;.the compound corresponding to Formula 1 3. melts at 130-132" C. The compound corresponding to Formula 4 may be prepared in analogous manner,

39 g. of 4-n-pr'opylamino-benzoic acid being used; it melts at 1 37 139" C. Polyphospho-ric acid can be used instead of oleum in the preparation of both compounds.

Y Example A paper foil is coated with a solution, and the other If it is de- 1 procedures fol-lowed, as in Example 4, except that in-the solution, one or both of the compounds corresponding to Formulae 3 and 4 are replaced by the same respective quantities of the compound 2,5-bis- [4 cyclo-pentylaminophenyl-(1)] 1,3,4-oxadiazole corresponding toFormula .5. This compound, which melts at 11812(l C., can be prepared by condensing 13 g. of hydrazine sulfate with 41 g. of 4-cyclo-pentylamino-benzoic acid in .250 g. of oleum in a manner analogous .to that given in Example 1 for the preparation of the compound of Formula 1. The

compound 4-cyclo pentylamine-benzoic acid is obtained when 68.5 g. of 4-amino-benzoic acid are dissolved with 33 .g. of potassium carbonate in .300 ccof waterand the solution is boiled for six hours under reflux with V 74.5 g. of cyclopentyl bromide. After the reaction mix-. ture has cooled, crystals are precipitated which are recrystallized from 96% ethyl alcohol. The 4-cycloentylaminoabenzoic acid melts at-128130 'C.

:7 Example 6 0.5 g. of 2,5-bis-[4'cyclohexylamino-phenyl-(1)]-1, 3,4-oxadiazole (Formula T6), 1 g. of 2,5-bis-[4.' -(di-npropyl) amino phenyl (1')] 1,3,4 oxidiazole (Formula 7) and 1 'g of resin-modified maleic acid resin (e.g., that marketed by Reichhold'Chemie AG, Hamburg, under the registered trade-mark Beckacite K i are dissolved in 30 g. of benzene and the benzene solutionis applied to a s'up'erficially-roughened aluminum foil. After the solvent has evaporated, thelayer left behind 'ad- 'herfes firmly to the "surface of the foil For the produca tion of an image, subsequent procedure is the same as de- 7 scribed in Example 1, a positive image. being obtained from a positive master; fixing is also carried out as described in Example. 1. To convert the image into a positive printing plate, the image side of the aluminum foil is wiped over with ethyl alcohol (96%), rinsed with water and rubbed in with greasy ink and 1% phosphoric acid.

2,5 bis [4' cyclohexylamino phenyl (1')] 1,3,4- oxadiazole (Melting Point: 186187 C.) can be obtained by condensation of 13 g. of hydrazinesulfate with 48g. of 4-cyclohexylamino-benzoic .acid in 260 g. of oleum (24% S0 in analogous manner to the compound corresponding to Formula 1, which is described in Example 1. 2,5 bis [4'(di n ropyl) amino phenyl- (1')]-1,3,4-oxadiazole (Melting Point: 137-138 C.) can be obtained from 13 g. of hydrazine sulfate and 48 g. of 4-di-n-propyl)-amino-benzoic 'acid in oleum, also in analogous manner to that in Example 1. 7

Example 7 0.5 g. each of 2,5 bis-[4-acetylamino-phenyl-(1')]-1,3, 4-oxadiazole (Formula 8) and 2,5-bis- [4-acetyl-amino-2' chloro-phenyl-(l')]-1,3,4-oxadiazole (Formula 9) together with 1 g. of resin-modified maleic acid resin (eg, that marketed by Reichhold Chemie AG, Hamburg, under the registered trade-mark Beckacite K 105) are dissolved in 30 g. of methylene chloride and the solution is'coated on to a paper foil of the same type asused in Example 1, and dried. The paper foil is 'then further processed for the production of an image'as described in Example 1. A positive image is obtained from a. positive master.-

In analogous manner to that described in Example 1 for the preparationof-the compound of Formula 1, 2,5-

bis [4 acetylamino phenyl (1')] 1,3,4 oxadiazole (Melting Point: 262-263 C.) can be obtained by condensation of 13 got hydrazine sulfate with 39 g. of

4-acetyl-amino-benzoic acid in 25C! g. of oleum (24% Example 6 The procedures of Example 7 are followed, except that in the coating solution, one or both of the compounds corresponding to Formulae 8 and 9 is or are replaced by the same quantities of 2,5-bis[4'-(n-propylamino)-2 chlorphenyl-(l) ]1,3,4-oxadiazole (Formula 10).

In analogous manner to that described in Example 1 for preparing the compound of Formula 1, 2,5-bis-[4- (n propylamino) 2' chloro phcnyl (1')] 1,3,4-

xadiazole (Melting loint: 132-140" C.) can be prepared by condensation of 13 g. of hydrazine sulfate with 45 g. of 4-n-propylaminc-2-chloro-benzoic acid in 260 g. of oleum (24% S0 Example 9 1 g. of 2,5-bis-[4-diethylarr1ino-phenyl-(1)]-1,3,4- oxadiazole (Formula 2) and 1 g. of phenol-modified synthetic resin (e.g. the resin produced by polycondensation and marketed under the registered trade-mark Rhenophen 140 by Rheinpreussen G.rn.b.H. Hombergam-Niederrhein) are dissolved in g. of benzene. This solution is coated on to a translucent paper (i.e paper which is light-permeable but not transparent), the surface of which paper has been pretreated against penetration of organic solvents, and the coated paper is dried.

The treated paper is electrically charged by means of a corona discharge and placed with its coated side against a page of a book which is printed on both sides and against the back or which page a sheet of black paper has been placed, and it is exposed for four seconds to the light of a 1G0-watt incandescent lamp, i.e., exposure takes place through the translucent paper. After the exposure, the reflex image is dusted over with a resin powder coloured with carbon black. A positive mirror-image with good contrast is obtained. firmly pressed upon the image so obtained, the image is transferred and a correct reading image is produced on .the paper or foil. in the production of the correct reading image an electric field can be applied in manner known per se to the paper or foil which is to receive the correct reading image. If the paper or foil is transparent, intermediate originals are obtained suitable for further reproduction, for example on photo-printing paper.

Example 1 0 1 g. of 2,5-bis-[4'-ethylaminophenyl-(1)]-1,3,4'oxad-iazole corresponding to Formula 11 and 1 g. of ketone resin (for example that known as Kunstharz EM marketed by Rheinpreussen G.1'l1.-0.H., Homberg-am-Wiederrhein) are dissolved in 30 g. of ethylene glycol-monomethyl-ether and the solution is coated on to paper and dried. For the production of an image, the coated paper foil is further processed as described in Example 1. From a positive master a positive image with good contrast is obtained.

2,5 bis [4' ethylamino phenyl (1')] 1 ,3,4- oxadiazole (Formula 11), with Melting Point 10161 C. can be obtained by condensation of 36 g. of 4-mono- N-ethylamino-l-benzoic acid with 13 g. of hydrazine sulfate in 250 g. of oleum (24% S0 in analogous manner to that described in Example 1 for the preparation of the compound of Formula 1.

Example 11 of the compound corresponding to Formula 12, 1 r ketone resin (e.g., the Kunstharz Eld mentioned in Example 8) and 0.01 g. of rhodaniine B (see the preceding table of dyestuffs) are dissolved in 30 g. of glycolethylene-rnonomethylether and the solution is coated on to paper and dried.

The sheet is charged by means of a corona discharge, and the thus sensitized paper is exposed for /2 second under a positive master to the light of a LOG-watt incandescent lamp and then dusted over with resin powder coloured with carbon black. A positive image is pro- If paper or plastic foil is l@ duced which is fixed by heating. colourless ground are obtained.

The compound corresponding to Formula 12, 2,5-bis- [4 N ethyl N n propyl minophenyl (1')]- 1,3,4-oxad-iazole with Melting Point 98 C. can be pre pared by condensation of 20.5 g. of 4-N-ethyl-N-n-propylamino benzoic acid with 13 g. of hydrazine sulfate in 250 g. of oleurn (24% S0 in analogous manner to that given in Example 1 for the compound corresponding to Formula 1.

The N-ethyl-l-n-propyl-amino-benzoic acid can be obtained in manner analogous to that described in Example 5 for the preparation of 4-cyclopentyl-amino-zbenzoic acid, a solution of 16.5 g. of 4-N-ethyl-amino-benzoic acid and 13.8 g. of potassium carbonate in cc. of water to which 12.3 g. of propyl bromide has been added being boiled under reflux for a number of hours.

Black images on a Example 12 Example 13 l g. of the compound corresponding to Formula 13, 1: g. of ketone resin (e.g., the Kunstharz EM mentioned in Example 8) and 0.02 g. of the cyanine dyestutf of the following structure:

H2O S-(]1Hg HZC G=OHCH=OH- E CH1 are dissolved in 30 g. of ethylene-g1yco1-monomethylether and the solution is coated on to paper and dried.

The sheet is charged by means of a corona discharge, and is then exposed for one second under a positive master to the light of a 100-watt incandescent lamp at a distance of about 15 cm. and then dusted over with a resin powder coloured with carbon black as described in Example 1. A positive image is formed Which is fixed by heating.

The compound corresponding to Formula 13, 2,5-bis- [4 N ethyl N acetyl) amino phenyl (1')]- 1,3,4-oxadiazole of Melting Point 156157 C. can be prepared from the compound of Formula 11, by boiling the same for four hours With acetic anhydride. When the reaction is complete, the resultant mass is poured on to water and after several hours the compound corresponding to Formula 13 precipitates out and after being rinsed with water is recrystallized from ethyl alcohol.

Example 14 1 g. of the compound corresponding to Formula 1, 1 g. of a zinc resinate (for example that known as Zinkresinate 357, produced by Lehmann & Crebert, Mannheim- Rheinau) and 0.02 g. of acid violet 7 EN (see precediug table of dyestuffs) are dissolved in 30 g. of ethylene glycolmonomethylether and coated on to paper and dried. A-fter the material has been charged .by means of a corona discharge the sensitized paper is exposed under a positive master for A second at a distance of approximately 15 cm. to the light of a IOU-watt incandescent lamp and then dusted over with a resin powder coloured with carbon black as described in Example 1. A positive image is form d that is fixed :by heating.

3,11 11. Example 15 The procedure described in Example 1 is followed, except that a solution of 1 g. of. the Compound correspending to Formula 11 and 1.5 g. of a polymerized natural resin (e.'g., the resin produced by the American firm Hercules Powder Company, Wilmington, and mar- 7 keted under the name Hercules Poly Pale) in 30 g. of

acne? ethylene glycolmonomethylether is used for coating paper. a

Positive images are obtained.

Instead of the above-mentioned resin produced by ,Hercnles Powder Company, a resin consisting chiefly of dimerised abiet-inic acid can be used (e.g., Hercules I Dymerex produced by the same firm) or a hydrogenated natural'resin (e.g., Hercules Staybelite also produced. by Hercules Powder Company).

Example 16 A paper base is coated with a solution of 10 g. of

5 after-chlorinated polyvinyl chloride (e.g., the plastic marketed by Dynamit AG, Rheinfelden, under the trade name Rhenofiex). in 100 g. of acetone, and dried. After drying, this paper is coated with a solution oil g. or" the compound corresponding to Formula 2 and 1 g. of f ketone resin (e.g., that known as Kunstharz AP produced by Chemische VJerkeI-liils AG, Marl) in 30 g.

' of ethyleneglycol-monomethyl-ether and further. processed amino-phenyl-( 1 -1,'3,4-oxadiazole -For'mula 14 and 1 g. of manila copal or other natural resin, are dissolved in 50 g. of ethyleneglycol-monomethylether.

as described in Example. 1.'

The paper is given a positive charge to sensitize the 'same, and is then exposed beneath a master at a dis- 5 tance of approximatelylS cm. to the light of a 100- 'Watt incandescent lamp; images with good contrast are 3 obtained after an exposure of only one second.

' Example 17 1( g. of 2- [4'diethylamino-phenyll) ]5- [4-dimethylcorresponding to The solution is applied to transparent paper and dried. Further procedure is as described in Example 1. The electrophotographically produced images are suitable as masters for the preparation of reproductions on any light-sensitive surfaces.

Instead of the compound corresponding to Formula 14,

2 [4dimethylamino-phenyl-(1')]-5-[4"-amino-3"-chloro-phenyl-( 1")]-1,3,4-oxadiazole, corresponding to Formula 17, may be used.

The compound corresponding 'to Formula 14 can be prepared as follows: Into a solution of 13 g. of hydrazine sulphate in 250 g. of oleum (24% S a mixture is introduc'ed consisting of 19.3 g. of 4-diethylamino-benzoic yacid and 16.5 g; of 4-dimethylamino-benzoic acid, the

temperature being maintained by cooling at approximate- Ily 25 C. The reaction mixture is then heated with stirring for four hours at 60 C. The reaction mixture is then. poured upon ice and made slightly, alkaline by the l addition with cooling upon ice and made slightly alkaline 1 by the addition with cooling of sodium hydroxide solution; the condensation product which then precipitates out is separated by suction, washed with water and purified by recrystallization from 80% ethyl alcohol. '[4' dimethyl-amino-phenyl(l')]-1,3,4-0Xadiazole (For- 2,5-bismula 1)-which is sparingly soluble is formed as a byproduct and is separated by repeated recrystallization of I the reaction product from 80% ethyl alcohol.

a I 2-[4'-diethylamino phenyl- 1') ]-5 [4"-dimethylamino-phenyl- (1 )]-1,3,4-oxadiazole -melts, after recrystallization, at f 158-160 C."

The compound corresponding to Formula 17 is oh- '1 .tained, in analogous manner to the compound corresponding to Formula 14, from 13 g. of hydrazine sulfate, 250 g. j of oleum (24% S0 and a mixture of 16.5 g. of 4-Cli- 1 methyl-amino-benzoic acid and 17.2 g. of 4-amino-3-chloro-benzoic acid. The compound corresponding to Forl :5 mula 17, 2- [4'-dimethylamino-phenyl- 1') -5- [4-amino- 3"-chloro-phenyl-(1'f)]-1,3,4-oxadiazole,, is obtained by repeated recrystallization of the reaction product from ethyl alcohol. It melts at 2l6217. C.

, Example 18 The procedure as in Example 1, is followed except that the paper-foil is coated with a solution of 1 g. of 2-[4'- mono n-propylarnino-phenyl- 1') -5- [4"-dirnethyl-aminophenyl-(l)]-1,3,4 oxadiazole corresponding to Formula 15 and 1 g. of2-[4--mono-npropylamino-phenyl-(1)1- 5 [4 monoethylamino-phenyl-(1")]-l,3,4-oxadiazole corresponding to Formula 16 in 30 g. of glycol-monornethyl-ether. Images electrophotographically produced erewith have very good contrast.

The compound corresponding to Formula 15 can be produced, in analogous manner to the compound corresponding to Formula 14, from 13 g. of hydrazine sulfate dissolved in 250 g. of oleum (24% S0 and a mixture of 17.9 g. of 4-mono-n-propylamino-benzoic acid and 16.5 g; of 4-dimethylamino-benzoic acid. The reaction prodmethylamino-phenyl-( 1") -l,3,4-oxadiazole is purified by fractional recrystallization from 80% ethyl 'alcohol and 1,3,4-oxadiazole, is purified by recrystallization from 80% ethyl alcohol; it melts at 126'-1 27 C.

Example 19 10 g. of after-chlorinated polyvinylchloride, eg. a product traded under the registered trademark Rhenofiex by Dynarnit-Actien-Gesellschaft (formerly Alfred Nobel & Co.) of Troisdorf, Rheinfelden, plants, are dissolved in g. of methyl ethyl ketone. To this solution there are added first 10 g. of the compound corresponding to Formula 1, dissolved in 50 g. of toluene, and then 0.011 g. of Rhodamine B extra (see Schultz, Farbstofftabellen, 7th edition, vol. 1, 1931, No. 864, page 365), dissolved in 2 g. or" methanol. This mixed solution, which has a kinetic viscosity of about 20.8 centistokes (17.1 centipoises) is. used for coating paper by means of a casting equipment in such a Way that a layer of about 6 microns in thickness is obtained. As-described in Example 1, direct images are produced on this paper by'an electrophotographic process. The degree of light-sensitivity of the paper is very high. By way of an episcopic processand using a.

light source of about 30 lux, good contrast images may be produced with an exposure of 1 second from originals printed on both sides.

Example 20 V 10 g. of a product obtained by subsequent chlorination I of polyvinylchloride, e.g.,' of the product sold under. the V registered trade-mark.Rhenoflex by Dynamit-Aktiengesellschaft, Rheinfelden, are dissolved in 100 g. of methylethyl-ketone. tion containing 10 g. of the compound corresponding to Formula 1 in 50 g. of toluene, then a solution containing 7 0.004 g. of ethyl violet (see iFarbstotitabellenP 7th edin, vo m v1 No. 787, page'33l), in 2 g. of methanol. The solution thus obtained, which has a kinetic viscosityof about 20.8 centistokes (17.1 centipoises), is used for mechanically coating a paper base. Advantageously the coat should have a thickness of about 6 To this solution there is added first a solumicrons. After drying the coated layer the paper is given a negative charge by means of a corona discharge, and then a latent image of a book page, printed on both sides is produced on the layer by an episcopic process. The layer side of the paper is then treated with a developer consisting of very small glass halls coloured by means of a very finely divided resin-carbon black mixture. The black resin adheres to those areas of the layer which during exposure were not struck by light, and a positive image becomes visible which is fixed by slight heating. The image has good contrast.

What is claimed is:

1. An electriphotographic material comprising an electrically conductive support layer and a photoconductive insulating layer, the latter containing a 2,5-his- (p-aminophenyl)-l,3,4-oxadiazole and a dyestufi sensitizer.

2. An electrophotographic material comprising an electrically conductive support layer and a photoconductive insulating layer, me latter containing a dyestuff sensitizer and a compound having the formula in which R, R R and R are selected from the group consisting of hydrogen, alkyl, cycloalkyl, and acyl radicals; and X and X are selected from the group consisting of hydrogen and halogen.

3. An electrophotographic material comprising an electrically conductive support layer and a photoconductive insulating layer, the latter containing a dyestufl sensitizer and a compound having the formula in which R, R R and R5 are alkyl radicals and X and X are selected from the group consisting of hydrogen and halogen.

4. An electrophotographic material comprising an electrically conductive support layer and a photoconductive insulating layer, the latter containing a dyestuif sensitizer and a compound having the formula it R2 in which R and R are hydrogen and R and R are alkyl radicals.

5. An electrophotographic material comprising an electrically conductive support layer and a photoconductive insulating layer, the latter containing a dyestuff sensitizer and a compound having the formula conductive insulating layer to light under a master and developing the resulting image, the photoconductive layer comprising a compound having the formula in which R, R R and R are selected from the group consisting of hydrogen, alkyl, cycloalkyl, and acyl radicals; and X and X are selected from the group consisting of hydrogen and halogen.

it). A process according to claim 9 in which the photoconductive layer contains a dyestuff sensitizer.

ii. A process according to claim 9 in which the photoconductive layer contains an organic colloid.

12. A photographic reproduction process which comprises exposing an electrically charged, supported photoconductive insulating layer to light under a master and developing the resulting image, the photoconductive layer comprising a compound having the formula R NN R2 M34 O R3 in which R and R are hydrogen and R and R are alkyl radicals.

16. A process according to claim 15 in which the photoconductive layer contains a dyestufi sensitizer.

17; A process according to claim 15 in which the photoconductive layer contains an organic colloid.

18. A photographic reproduction process which comprises exposing an electrically charged, supported photoc onductive insulating layer to light under a master and developing the resulting image, the photoconductive layer comprising a compound having the formula in which R and R are hydrogen and R and R are acyl radicals.

19. A process according to claim 18 in which the photoconductive layer contains a dyestufi sensit ler;

A process according to claim 18 in which the photoconductive layer contains an organic colloid.

21. A photographic reproduction process which cornprises exposing an electrically charged, supported photoconductive insulating layer to light under a master and developing the resulting image, the photoconductive layer comprising 2,5-bis-(4'-dimethylaminophenyl-(1') )-1,3,4- oxadiazole.

22. A photographic reproduction process which comprises exposing an electrically charged, supported photoconductive insulating layer to light under a master and developing the resulting image, the photoconductive layer comprising 2,S-his-(4-diethylaminophenyl-(1') )-l,3,4-oxadiazole. 23. A photographic reproduction'process which coniprises exposing an electrically char ed, supported photoconductive insulating layer to light under a master and developing the resulting image, the photoconductive layer comprising 2,5 bis-(4-isoarnylaminophenyl-(1) )-1,3,4 oxadiazole.

24. A photographic reproduction process which com 1 prises exposing an electrically charged, supported photo- 'conductive insulating layer to light under a master and developing the resulting image, the photoconcluctive layer comprising 2,5 bis (4'-- cyclopentylaminophenyl-(1) 1,3,4-oxadiazole.

25. A photographic reproduction process which'comprises exposing an electrically charged, supported photoconductive insulating layer to light under a master and developing the resulting image, the photoconductive layer 1 comprisin g 2,5 -bis- 4-cyclohexylaminophenyl-( 1) l 3 ,4- oxadiazole.

26. A photographic reproduction process which com- ;pri ses exposing an electrically charged, supported photoconductive insulating layer to light'under a master and developing the resulting image, the photoconductive layer comprising 2,5-bis-(4-(di-n-propyl)-aminophenyl-( 1') 1,3,4-oxadiazole. r

27. A photographic reproduction process which comprises exposing an electrically charged, supported photoconductive insulating layer to light under a master and deveioping the resulting image, the photo-conductive layer comprising 2,5 bis (4' acctylanunophenyl-( l) )-l,3,4

oxadiazole. a

' 28. A photographic reproduction process which comprises exposing an electrically charged, supported photo- "conductive insulating layer to light under a master and developing the resulting image, the photoconductive layer comprising 2,5-bis-(4'-acetylamino 2'-chlorophenyl- (1))'-1,3,4-oxadiazole.

29. A photographic reproduction process" which comprises exposing an electrically charged, supported photo- Jconductive insulating layer to light under a master and developing the resulting image, the photoconductive layer comprising 2,5 bis (4' n-proplamino) -2-chlorphenyl- "(1') -l,3,4-oxadiazole,

39. A photographic reproduction process which com- ,prises exposing an electrically charged, supported photo- -conductive insulating layer to light under a master and developing the resultingimage, the photoconductive layer comprising 2,5 his (4 ethylarninophenyl-(l) )-1,3,4-

oxadiazole.

' 31..A photographic reproduction process which comprises exposing an electrically charged, supported photoconductive insulating layer to light under a master and developing the resulting image, the photoconductive layer comprising 2,5 bis (4-N-ethyl-N-n-propylaminophenyl- (1') )-1,3,4-oxadiazole.

' 32. A photographic reproduction process which cornprises exposing an electrically charged, supported photo- 'conductive insulating layer to light under a master and developing the resulting image, the photoconductive layer 7 comprising 2,5 bis (4'-(N-ethyl-N-acetyl)-aminophenyl+ (1' );'l,3,4-oxadiazole.

" 33. A photographic reproduction process which comprises exposing an electrically charged, supported photoconductive insulating layer to light under a master and I developingthe resulting image, the photoconductive layer comprising 2 (4' diethylarninophenyl (1') )-5-(4-dimethylarninophenyl 1 1 ,3,4-oxadiazole.

34. A photographic reproduction process which comprises exposing an electrically charged, supported photo- A conductive insulating layer to light under a master and developin'gthe resulting image, the photoconductive layer i comprising 2 (4-dimethylaminophenyl-(1))-5-(4"-amil'lO-J -chlorophenyl-( l) )-1,3,4-oxadiazole. V 35.v A photographic reproduction process which com- 'conductive insulating layer to light 'under a master and developing the resulting image, the photoconductive layer comprising 2- (4'-mono-n-propylaminophenyl-( 1) )-5 (4- monoethylaminophenyl-(1") ).-l ,3 ,4-oxadiazole;

37. An electrophotographic material comprising an electrically conductive support layer and a photoconductive insulating layer, the latter containing a 2,5-bis-(paminophenyl)-l,3,4-oxadiazole and an organic colloid,

38. An electrophotographic material comprising an electrically conductive support layer and a photoconductive insulating layer, the latter containing an organic colloid and a compound having the formula in which R, R R and R5 are selected from the group consisting of hydrogen, alkyl, cycloalkyl, and acyl radicals; and X and X are selected from the group consisting of hydrogen and halogen.

39. An electrophotographic material comprising an electrically conductive support layer and a photoconductive insulating layer, the latter containing an organic colloid and a compound having the formula in which R, R R and R are alkyl radicals andrXiandt X; are selected from the group consisting of hydrogen and halogen. Q j

49. An electrophotographic material comprising an electrically conductive support layer and a photoconductive insulating layer, the latter containing an organic colloid and a compound having the formula 31 O Ra in which R and R are hydrogen and R and R are alkyl radicals. 7

41. An electrophotographic material comprising an electrically conductive support layer and a photoconducive insulating layer, the latter containing an'organic colloid and a compound having the formula in which R and R are hydrogen and R and R are acyl radicals. V a 7 References Cited by the Examiner UNITED STATES PATENTS 2,663,636 12/53 Middleton.

2,692,178 10/54 Grandadam 2,765,304 10/56 Siegrist et al; 260307 X 2,800,559 7/57 Ubbesolde.

2,825,814 3/58 Walkup 961 X (one; references on following page) Hart 252-5l0 17 1S FOREIGN PATENTS Deribere, Applications Pratiques de la Luminescence, 134,610 6/47 Australia. (1938) Pages 151452- Zchodro, I. Chim. Phys., vol. 29, pages 59-64 (1929). 4/56 Australa' Petrikaln, z. Phys. 0116111., v01. 10B, pages 9-21 1930 THER Vartanian, Physiochimica, VRSS vol. XXII, No. 2, Kallm t 1 Ph I IS I M N 6 5 Pages 201-224 (1947) am e a yslca evlew, v0 0. pages G. Przmary Exammer.

Winslow et 21., 1011111. Amer. Chem. Soc., vol. 77, pages PHILIP E. MANGAN, MILTON STERMAN, HAROLD 4751-4756 (Sept. 1955). N. BURSTEIN, Examiners. 

1. AN ELECTRIPHOTOGRAPHIC MATERIAL COMPRISING AN ELECTRICALLY CONDUCTIVE SUPPORT LAYER AND APHOTOCONDUCTIVE INSULATING LAYER, THE LATTER CONTAINING A 2,5-BIS-(P-AMINOPHENYL)-1,3,4-OXADIAZOLE AND A DYESTUFF SENSITIZER 